I wonder if the film influenced how people see Atticus. Maybe book Atticus is supposed to be more racist than movie Atticus, and most people are remembering movie Atticus, not book Atticus.
In my case I don't remember the book well enough to remember most of it. I read* it more than half my lifetime ago in English class as a teenager, in a country that wasn't the US, without access to the dispersion of ideas (the 90s Internet was much less discoverable) we have today. I remember Scout in the early chapters far more than I remember Atticus because I too was broadly speaking a tomboy and thought of myself as smarter than my teachers. I identified with her. I imagine the whole "smarter than teacher" thing struck a lot of kids more than the big important message. However, I do still remember the jail scene and the gist of the closing arguments from Atticus. Around the same time, I saw A Time to Kill (I think at home on tv) and remember the closing arguments in that. And at some point, I think in history class, we also studied Mississippi Burning. These three things specifically stick in my mind when I think of race in the US^, and influence me even today. So perhaps the book did get lost to the movie version for some people, but as a non-US kid in the 90s, I think a lot of it went over my head. I think I'm going to go back and read it again.
* I'm pretty sure I didn't Cliffs Notes this one, but I can't remember for sure. I don't remember seeing the movie, we might not have.
^ I don't think we ever really got introduced to the other racisms that the US has, eg Hibernophobia (irish), Italophobia, anti-semitism, etc, but I did learn about these from TV http://strawburry17.com/wp-content/uploads/2014/04/maggie-simpson.gif